Process for producing fuel oils having improved radiation emission



' pentane.

precipitation of the radiation emitting particles with PROCESS FOR PRODUCING FUEL OILS HAVING IIVIPROVED RADIATION EMISSION Warren C. Simpson, Berkeley, -Calif., assignor to Shell Oil Company, New York, N.Y., a corporation of Delaware N Drawing. Filed Sept. 15, 1958, Ser. No. 760,868

'5 Claims. (Cl. 208-) The present invention relates to the operation of furnaces in which fluid fuels are burned. More particularly, it is concerned with a method of improving and controlling the radiant heat or emissivity of flames produced in furnaces.

In many types of furnaces wherein the fuel burned is oil, gas, or mixtures thereof, at least a part of the heat released by the flame is transferred from the flame to the body being heated by means of radiation. This either occurs directly, as in the case of a solid charge, or indirectly, as in the case of a liquid charge. Open hearth steel furnaces, lime and cement kilns, annealing furnaces, tube still heaters, cracking furnaces, and the like are examples of many types of furnaces largely dependent upon radiant heat transfer. The present invention is especially directed to the operation of open hearth furnaces in steel making processes, but the principles and process apply to these other types of furnaces as well.

In all of such types of furnaces, the proportion of heat transferred to the charge by radiation is largely fixed by the design of the furnace and by the characteristics of the flame. For example, in an open hearth furnace nearly all of the heat is transferred to the charge by radiation. In the usual case of a tube still heater or kiln to which the charge is continuously fed at a constant temperature and rate, the proportion of radiant heat transfer depends upon the ratio of the tube surface area which the flame sees to the tube surface area cation is a continuation-in-part, Serial No. 641,874, filed February 25, 1957, now Patent No. 2,913,043, describes the improvement in radiation of residual fuel oils by precipitation of asphaltogenic bodies with relatively low molecularweight precipitants, such as kerosene, lower molecular weight paraflins down to and including butane and While these materials are satisfactory for the which that and the present invention are both concerned, it will be realized that the use of such precipitants involves increased cost of fuel oil components, since kerosene and the lower hydrocarbons have a higher unit cost than the relatively inexpensive residual fuel oils.

Consequently, a major object of the present invention is to provide a method for controlling the radiation effect within furnaces at a lower cost than heretofore possible.

Patented Sept. 13, 1960 It is a more particular object of this invention to provide increased flexibility in the radiation effects of flames burning in the furnaces. It is a further object of the present invention to reduce the cost of operating such furnaces not only with respect to fuel components but with respect to the time necessary for causing the required degree of heating of the materials being subjected to the heat evolved in and by such furnaces. Other objects will become apparent during the following detailed discussion of the invention.

Now, in accordance with the present invention, it has been found that the radiation or emissivity (in the infrared spectral region) of a flame burned in a furnace may be increased by mixing two incompatible residual fueloils, proportions thereof mixed in quantities at least sulficient to cause precipitation of high molecular weight asphaltogenic materials, namely, those having molecular weights above about 1,000 (preferably 1,000-5,'000) present in at least one of the residual fuel oils and thereafter burning the fuel containing said particles, whereby flames of increased emissivity are obtained. The two residual fuel oils are employed in volume proportions between about 1:4 to about 4:1, and preferably are mixed in volume proportions of between about 25-75% and -25% More particularly, the present process comprises the mixing of at least two residual 'fuel oils, which each 'individually may show no evidence of precipitation of asphaltogenic particles thereim imsuch proportions that asphaltogenic particles are precipitated. The precipitation is based upon the relationship of the precipitating tendencies of the asphaltogenic materials present in the residual oils and the solution power of the cutter stock formed by the blend of two or more residual .fuel oils containing the same.

Residual fuel oils generally (but not always) consist of a blend of vacuum flashed or thermally cracked residue oil in a mixture of lighter distillates commonly referred to as cutter stocks of'relatively low viscosity. When the aromatic or heteroaromatic components of the residue having molecular weights greater than about 1000 are maintained in true solution by the lower molecular weight aromatics and .hetemaromatics in the system, the fuel oil will be optically clear-when examined in thin layers. When the solubilizing power of the lower molecular weight components of the residual fuel oil is not suincient to maintain true solution, the occurrence of' molecular association between various of the higher mo lecular weight polar components leads to the formation of loose aggregates of molecules into clusters which eventually grow into aggregates .sutficiently large to be visible to the unaided eye as a precipitate. The principle effect of the present invention is to adjust the balance of precipitatable materials with solvating materials in such a way as to cause the desirable type of precipitation for the purpose of later burning to effect an increase in radiation of the flame.

In the discussion of the aspects of the invention which follow, reference frequently will be made to two terms, namely, precipitation index and solvency index. The precipitation index is defined as the volume percentage concentration of alpha-methyl naphthalene plus residual fuel in a mixture with cetane that causes incipient precipitation of the residue. For this test a solution of the residue in alpha-methyl naphthalene is made containing about 10% residue. A small drop of this solution is taken with a wire or rod and placed on a piece of filter paper. (Smooth hard porous paper such as Wh-atman No. .50 is preferable.) This will normally soak into the paper and leave a fairly uniform brown area about /2 to inch in diameter. If, however, a dark brown or black ring or spot the size of the original drop remains, that indicates the presence of coke particles (as in the Oliensis test) and the solution should be filtered. One or two milliliters of the solution, filtered if necessary, is pipetted into a test tube or vial. Cetane (n-hexadecane) is added in measured increments to the measured volume of solution. After each increment is added the vial is stop-' pered, shaken, and a small drop of the solution removed and placed on the filter paper. The cetane is conveniently added from a 5 ml. buret, and the size of the increments will depend on the accuracy desired in the determination. A series of spots on filter papers will then be obtained representing solutions of the residue in a series of mixtures of alpha-methyl naphthalene and cetane.

Examination of these spots will reveal a certain ratio of the two solvents at which a darker ring or spot the size of the original drop is superimposed on the brown area on the filter paper. At higher cetane concentrations the ring or spot becomes more pronounced; at lower concentrations it is absent. The point at which the ring starts to appear, then, is that point at which the total mixture is of barely adequate aromaticity to dissolve the least soluble component of the residue. The volume percentage concentration of alpha-methyl naphthalene plus residue fuel in the total mixture with cetane that causes incipient precipitation of the residual fuel oil is designated as the precipitation index of that residue. It has been found that this value can usually be determined reproducibly to less than one unit.

Cutter stocks and solvents for asphaltogenic residues can be evaluated on the same basis as residues by this test method. In this case one or the other of the two standard solvents, namely, cetane or alpha-methyl naphthalene, as determined by preliminary test, is replaced by the cutter stock and a precipitation point is determined using a residue whose precipitation index has been found by the standard procedure. A residue or fraction of high asphaltene content relatively undiluted with non-asphaltic constituents is preferred as a standard for the test. Thus, a mixture of cutter stock in one standard solvent is found that is equivalent to a known mixture of alpha-methyl naphthalene and cetane with respect to a given residue or sample of asphaltenes, from which information the solvent power of the cutter stock can be expressed in terms of the volume percentage of alphamethyl naphthalene in a mixture 'of the same with cetane that has the same solvent power as the cutter stock. This is termed the solvency index of the cutter stock.

Since the test as applied to residues measures the point of incipient precipitation of the least soluble component in relatively dilute solution, any addition of more soluble materials to a residue (or the more soluble constituents of the residue itself) has little effect upon the precipitation index. Therefore, the precipitation index can be determined on a blended fuel just as well as on the residue itself. On mixing two incompatible fuels, the precipitation formed is the least soluble material in the mixture, which will normally come from only one of the fuel oils. The precipitation index of the mixed fuel will therefore be the same as that of the fuel containing the least soluble component. On the other hand, although each stable fuel may contain cutter stock that is adequate for its own lease soluble component, a blend of the two cutter stocks would have average solvent powers. In the case of incompatible fuels, these properties are inadequate for the least soluble asphaltenes in the mixture. Consequently, the basis of the present invention comprises the utilization of these physical observations so as to controllably produce precipitation of asphaltogenic materials for the purpose of subsequent combusion and increase in radiation of the flames so produced.

The residual oil forming the asphaltogenic oil component of the subject fuel oils may be straight run or cracked Petroleum residues. Typical species of these naphthenic residues which likewise have low precipitation indices, mildly cracked asphaltic residues having intermediate precipitation indices and severly cracked residues having relatively high precipitation indices. The residual oils forming the heavier component of the subject fuel oils have precipitation indices greater than 25 or 30 and preferably have precipitation indices bearing between about 35 and about 80. Normally, these will be between about 40 and about 75 and ordinarily it is preferred that fuel oils be combined which have residual oils differing approiu'mately at least about 10 units in precipitation index numbers. In a preferred embodiment, a first residual oil containing an uncracked tresidual oil possessing a precipitation index of about 30-40 is mixed with a second residual fuel oil containing a cracked residual oil possessing a precipitation index of about 45-80. Residual fuel oils forming the heavy component of the fuels normally have the following characteristics:

Penetration-'0 to 1000 (the higher values (500- 71,000) from distillation and thermal cracking-the lower values (0-500) from vacuum flashing) Softening point-l40 to 32 F. Flash point-1S0 to 450 F.

Typical residues Flasher Bitch Percent sulfur The cutter stocks with which these residual fuels are combined are lower boiling distillate materials normally of petroleum origin which serve the dual purpose of reducing the viscosity of the fuel oil and at the same time maintaining a substantially homogeneous composition; Under previously known circumstances it was believed to be desirable to burn substantially homogeneous fuels so as to prevent plugging of outlet nozzles and the like. Moreover, the uncontrolled and unplanned-for precipitation of asphaltogenic materials results in agglomeration as a sludge which is entirely undesirable and would be useless for operation of the present invention. In order to be successful, the precipitated particles must be formed in a highly dispersed form having an average maximum particle diameter of between about 0.5 and about 150 microns each. Particles smaller than or larger than these desired limits caused reduced amounts of radiation of a burning flame to occur.

The cutter stocks, therefore, which may be utilized in the asphaltogenic residual fuels are those which have a higher solvency index than the precipitation index of the residual oil components of the fuel. This is normally essential in order to produce a homogeneous fuel composition. The solvency index of the most preferred cutter stocks is normally between about 35 and as determined by the procedure given hereinbefore. Suitable cutter stocks include petroleum aromatic extracts, such as furfural extract of catalytically cracked gas oil, Edeleanu extracts of various boiling points such as that from 375 to 590 or from 500 to 650 F., aromatic extracts from flashed pitch, light catalytically cracked gas oil, clarified oil, heavy catalytically cracked gas oil and the like.

West West LA. LA. Texas Texas Basin Basin Light Heavy Cat. Clarified Cat. Cat. Cracked Oil Cracked Cracked Gas Oil Gas Oil Gas API gravity 20. 8 11.0 31.2 26.6 Percent sulfur 1.08 1.02 0. 32 0. 70 Diesel index 41.1 42. 2 ASIM distillation, F

I.B.P 425 454 408 488 F.B.P 715 760+ 470 568 l0% 487 526 514 624 50% 526 64.2 574 680 619 -618 700+ Percent recover 98 85 99.0 97. 0 Pour point, I 5 55 Percent Ramsbottom carb 0.08 0. 24 Solvency index; 54 52 36 Viscosity, SSU, at 100 F.... 37 71 Aniline point, F 93 101 It will be understood that the residual fuel oils may vary widely in their two components and in the combination of the two components, namely, in the residual fuel itself, in the cutter stock itself and in the combinations which may be made of these two components. For example, with a residual oil having a relatively low precipitation index, such as an uncracked highly parafiinic or an uncracked naphthenic type residual oil, it is possible to select a cutter stock from a much Wider variety of distillates than is possible with residual fuels having higher precipitation indices. This is possible since most cutter stocks possess solvency indices high enough to main- V tain homogeneity almo'st'all 'rlatively'low precipita tion index residual oils. However, as the precipitation index of a residual oil increases, the possibility of selection of cutter stocks which will maintain homogeneity therewith becomes more and more restricted. The selection of a cutter stock will depend upon not only the precipitation index of the residual oil but also upon the viscosity, pour point and flash point desired in the final residual fuel oil composition.

The proportion of residual oil to cutter stock in the fuel oil composition will vary Within relatively wide limits but normally will be between about 25 and 75% cutter stock, the balance of the composition being the residual oil. Another limitation on the percentage of cutter stock will be the minimum concentration of cutter stock necessary to insure that the individual residual fuel oils will be homogeneous until they are purposely mixed for the object of producing a desired type of particle dis persion just prior to burning.

Having selected the individual initially homogeneous residual fuel oils to be combined for the pun-pose of precipitation of particles it then becomes necessary to determine the proportion of each oil to be used in order to insure precipitation. This can be readily calculated in accordance with the following method:

-A state of incipient precipitation exists when the solvency index of a blend of fuel oils just equals the precipitation index of the most insoluble residue in the blend. This may be stated as follows:

(Vsca) (SIcsa) (Vcsb) (SIcsb) Vcsa-l- Vcsb slblend: PIh

where:

Then 1-X=volume fraction of cutter stock b in the cutter stock portion of the fuel blend. Then the equation can be rewritten as follows:

Solving for X we have:

Ph-Sl'csb SIcsa-SIcsb In a practical example the volume fraction (X) of one of the cutter stocks in the cutter stock portion of the blend is first calculated. Then from the cutter stock content of the fuel and the volume fraction X, the actual volume percent of this fuel in the blend is calculated.

As an example the calculation for blends of fuels A and B in Table I Will be made. The percentage of fuel A required to produce precipitation in the blend will be deter-mined.

SI =36, SI =56, PI =45 =volume fraction of cutter stock A' 0.45 -03 volume of fuel B Then the percent'of file] A in the blendis A+B 0.s4+0.9 114 48% When the amount of fuel oil A in the blend is this amount or greater, precipitation will occur.

Having determined the precipitation index of two fuels and the solvency index of the cutter stocks contained therein, it is possible to calculate the combined composition of the two which will give an assurance of precipitation of particles. In each case, as the working examples given hereinafter will show, it is necessary to mix a sufficient amount of one residual fuel oil with a second and different residual fuel oil in such proportions as to obtain a mixture of cutter stocks having a solvency index which is numerically lower than the precipitation index of the residual oil most prone to precipitate, namely, the residual oil having the highest precipitation index. Under these conditions, precipitation will occur and when the mixed fuel is burned will result in increased radiation thereof.

In accordance with a preferred version of the present invention, the precipitated particles (including agglomerates of originally discrete particles) are distributed in particle size over a range from about 0.5 micron to about 150 microns, so that as the relatively smaller par ticles are consumed and disappear from the fiame, the rela- 60 tively larger particles still persist in acting as radiating bodies. In accordance with one phase of the present in vention, this range in particle size of the precipitated particles may be elfected by .a differential time of particle size existence between several portions of the residual fuel being introduced into the furnace. 'If, for example, the smallest particles are formed by a residence time outside of the furnace and prior to burning of about 5 seconds or less, then it is preferred that an appreciable portion of the fuel oil be subjected to precipitation techniques for a time prior entrance into the furnace of at least about 30 seconds or more, so that the necessary time for particle growth is gained after which both particle-containing residual fuel streams are introduced, either together or separately, into the flame-burning area.

Since it is preferred that substantially continuous eleing process, and varying vated emissivity throughout the entire area of the flame is obtained, it is preferred that at least about 10% by weight of the precipitated particlm having diameters less than about 0.5 microns and at least 10% by weight of the particles have diameters greater than about 10 microns. Thus, there is virtual assurance that the flame will contain at all times an emission-improving portion of radiating particles, even though the flame be of a length from about several inches to as much as 35 feet. Flames from about to 30 feet are commonly employed in such large scale industrial installations as open hearth steel furnaces and the like. The upper limit of particle size is determined as that size particle which will just be consumed in the particular flame whose length, temperature, percent excess air and linear velocity are known. For any given flame and a knowledge of the furnace geometry this maximum particle size can be determined.

The fuel oils to be treated in accordance with the pressteel making furnaces, comprises maintaining the flame profile substantially constant during the entire steel makthe radiation of the flame by controlling the proportion of suitable particles in the fuel stream. A still further improvement in this respect comprises maintaining the total fuel input substantially constant throughout the steel making process, thus maintaining the flame profile substantially unaltered during the same period, but varying the radiation characteristics thereof by variation in particle proportion.

The open hearth furnace is a batch furnace. Steel scrap, pig iron, and sometimesaasmallrll lm fiil lil m are charged to the furnace, melted and refined. In the first stage of the melt, the charging period, the solids are cold and present an irregular surface to the flame and combustion gases. The actual charge to the furnace is normally carried out in a series of steps since the unmelted mass usually is too large for the entire charge to be made at one time. Consequently, substantially half of the charge is inserted in the furnace and partially or fully melted before further portions of the charge are added. Upon commencement af heating at least a por tion of the charge melts sufficiently to substantially submergethe remaining solids and the surface of the charge becomes flat. When this stage has been reached, the so-called melting period begins. When the ingredients have all reached the melt stage (or substantially so), the refining period starts, during which the liquid charge is maintained at a high and substantially constant temperature for the necessary time to complete purification by separation of the slag from the main body of the melted steel.

It is economically desirable to minimize the time consumed during the charging and melting periods in order to maintain a high rate of production of steel from the furnace. During these first two periods (charging and melting) the temperature is being raised continually and, consequently, during this time the maximum degree of radiation from the flame is desirable. The maximum fuel input rate is limited by the melting temperature of the roof of the furnace as well as the optimum flame profile for eflicient transfer of heat from the flame to the melting charge. During the charging period high fuel input rates may be employed when both the charge and the furnace refractory roof are relatively cool. However,

during the melting period, the fuel input rate is limited by the maximum allowable temperature of the refractory roof which is ordinarily in the order of 2800-3000 F.

Since the temperature of the charge during this period gradually rises from 2400 to 2600 F., there is a very small margin between required and maximum allowable furnace temperatures.

While the fuel input rate can be varied, it will be obvious that the flame profile will alter radically with any change made in this input rate. Hence, it is desirable to establish the optimum flame profile for a given rate of fuel input and thereafter maintain the same rate of total fuel consumption. The present process is based upon these considerations and provides the flexibility necessary for successful operation thereof.

Fuels have been modified in the past by the incorporation of solid fuel materials, especially powdered coal. However, the use of powdered coal in fuel oil suspension does not provide the desired increase in radiant heat,

since the powdered coal particles are either relatively extremely coarse and consequently do not present the surface area necessary for optimum black body radiation, or (due to burning rates slower than that of oil) must be ground much finer than precipitated oil particles if they are to be completely consumed. Other solid fuel components used as proposed heretofore, have been incorporated in the entire body of the fuel oil and consequently permitted no latitude inthe alteration of the radiation of the flame which must necessarily have remained at a constant value for any total rate of fuel input. experienced wtih these prior art coal and carbon black suspensions comprised the difficulty of maintenance of the suspension, since in the relatively dilute form in which they are normally employed the particles are not self- Moreover, the principal disadvantage which was supporting and tend to settle out. This property may overcome in part by incorporation of certain suspending agents and surfactants, but this is an uueconomical means of creating and maintaining the suspensions and also entails certain problems such as the creation of undesirable ash. Since the fuel input into a large furnace V, such an open hearth furnace is extremely high, the ash problem becomes serious due to de'positiondhereof on the sides of the furnace and the operating parts thereof.

The improvement caused by this invention is apparently based upon the increased emission of radiant energy at wave lengths at which solid matter absorbs most efliciently, i.e., in the infra-red range.

The mixture of fuel oils is selected so as to produce precipitated particles in an amount between about 1% and about 10% by weight based on the total fuel.

The effect of increasing the emissivity of the combusting fuels is of great economic significance since it has been ascertained that the average time of completing a run in a standard commercial open hearth furnace can be reduced as much as about 10%.

The addition of the first fuel oil to the second residual fuel oil is preferably effected just prior to injection into the furnace and combustion of the fuel composition. The timing will be adjusted to produce the optimum size of particles in accordance with the limitations set forth hereinbefore but normally will be between about 1 second and 24 hours and preferably between about 30 seconds and one-half hour. The production of particles in a residual fuel, according to the present process, results in substantially spherical particles which, upon aging in the fuel oil composition, tend to agglomerate into larger bodies which still maintain their essentially spherical shape. This is sharply differentiated from the chain-like agglomerates Whch are created upon the aging of carbon black particles suspended in fuel oils.

In order to maintain a substantially constant supply of radiating precipitated bodies throughout the entire length of a fuel flame such as in an open hearth furnace, it is preferred that the particle size distribution be spread between the limits already stated, namely, between about 0.5 micron and about microns. This may be diflicult to attain if the first fuel oil is added to the second oil being fed to a burner at two or more time units prior particles in any proportions. A blend of equal quantities to burning so that an elapsed time is permitted for part of fuels A and D results in a desirable precipitate being of the particles to agglomerate or grow and form the formed. relatively coarser varieties which have a more extended It is possible to predict incompatibility and therefore life prior to being completely burnt in the flame during precipitation of radiation emitting particles of fuel oil combustion. The two or more portions of the combined blends in advance from the precipitation index values of fuel may be commingled at the burner or may be injected the residues, the solvency index values of the cutter into the combustion area'through separate nozzles. An stocks and the quantity of the cutter stock in each fuel. aging opportunity can be created by passing that portion Table II which follows shows the results of calculating of the fuel oil in which the relatively larger particles the solvency index values of blends of equal volumes of are to be formed into a storage tank preferably containvarious of these four fuels and states the stability or ining agitation means or through a coil designed to increase stability of the blend on the basis of data. For example, the residence time of the fuel oil therein so as to provide a 50-50 blend of fuels A and B results in a precipitate the necessary extended particle formation period prior being formed. Because the solvency index of the cutter to burning stock in this blend is 39, which is less than the precipita- Y utilization of the Present Process of precipitating tion index of 45 for the least soluble residue in the blend, fuel components in the fuel Stream Of Such furnaces, i it is also possible to calculate the minimum amount of s been found that great eeOllOmiC advantages can he fuel A required to cause precipitation offuel B and this Obtained, for p in the cycle time for the Pm is also shown in Table II to be at least 48% by volume tion of steel. By the precipitation of 1.5-5 insoluble f fu l A bl nd, I particles into the fuel oil utilized for the heating of an Fuels A and C are stable in all proportions because Open hearth furnace, for p during the charging the lowest solvency index of the pair is higher than the and melting stages but not during the fi g g a highest precipitation index of the residues in the pair. 10% reduction in total cycle time can he achieved- Y The same is true of blends of fuels B and C. Blends of maintaining the total fuel input constant during the entire fuels A and D result in a precipitate being formed when period of steel production (or during any other comthe blend contains at least 22.5% by volume of fuel A- Parable P s as cement production) the tim Fuel oil D may be caused to precipitate by blending with profile was substantially unaltered, but the radiation 44% o more of fuelsB'or C. th f s a i al y h ng d y t igig tignvegenie: The quantity-of precipitate formed is roughly proper I 31011 of the hreeiPltated' fuel partieles- The increased tional to the asphaltene content of the residual -fuel and i F luminoslty l not appear to affect refractory life to the difference between the precipitation index of the m h furngtees slhee the temperature of the time W least soluble residue and the solvency index of the final not substantlally dlfierent from that of the flame Y fuel oil blend. When portions of the blended fuels A out partlcle formation. The following examples lllusand B and f the blended fu ls A and D are burned, trate the process of the present invention. the resulting flames exhibit substantially increased f i enableq the of 40 emissivity due to the formation of the precipitate as comflarnes ofhlgher radiation frombaslcally low cost resldupared with the burning f the individual f l a1 fuel oils. Thus, it is especially distinguished in this respect from prior ant high emissivity compositions wherein materials were added for the purpose of in- Table I creasing emissivity but only by means of increasing the cost of the total fuel compositions as is true even in 'the I A case of the addition of lower molecular weight distillate Type of Residual Fuel Ohm A B C D materials, such as kerosene or gaseous preclpitants, such as butane. Consequently, the present invention utilizing llig very ll? y Severely the physical properties of precipitating tendencies and s x M y p Cracked limited solvation. tendencies of the asphaltogenic ma- Parammc Cracked theme terials and of the cutter stock, respectively produces the same desirable degree of increased radiation but at no gravity 2&4 ,6 6,3 increase in cost of the total fuel oil components since Penskey-Mertens 33 260 190 202 196 each of the residual fuel oils has the same basic low 2% 31 3?; Pee and no Premium Pee medals are asssrllssraie 2:3 2:3 2:2; 12;: EXAMPLE I tiltfilii hsanistssait H95 593 i??? if? Table I which follows shows the properties of four 35 45 (I) 77 residual fuel oils. Each of the fuels is stable -by itself 1 S v y index f utter and shows no precipitation of the particles. This is in gg 'h ighg 'ggggigjj11:: 32 8 38 accordance with the relative precipitation index and the solvency index of the cutter stock in each fuel. It will lstable be noted that the solvency index of the cutter stock in Table II STABILITY OF FUEL OIL BLENDS CALCULATED FROM PROPERTIES OF THE FUELS Fuel Oil Combinations A and B A and 0 A and D B and C B and D O and D Solvencyindex of 50-50 blend 39 39 62 56 75. Precipitation index of least soluble 45 35 77 45 77- 77.

St1i1bi 50-50 blend Unstable Stable Unstable Stable Unstable Unstable. Minimum concentration to insure At; least 48% A Stable in all At least 22.5% A Stable in all At least 44% B At least 44% C.

precipitation. proportions proportions.

9 fuel oil at only one particular time prior to combustion of the fuel oil composition. Therefore, in accordance with one phase of this invention, it is a preferred process to inject portions of the first fuel oil into second fuel 16 each case is higher than the precipitation index of the fuel. However, a blend of equal quantities of fuels A and B results in precipitation but combinations of fuels A and C are compatible and show no precipitation of I claim as my invention:

1. A method of improving the radiation emission of asphaltogenic residual fuel oils during combustion thereof which comprises mixing two residual fuel oils, each fuel oil comprising a residual oil and a distillate cutter stock having a solvency index of 35-95, at least one of the residual oils having a precipitation index greater than the solvency index of the combined cutter stocks, said fuel oils being mixed in proportions between about 1:4 to about 4:1 on a volume basis, said proportions being sufficient to precipitate between about 1% and about by weight of the total ffi'el' components ashigh molecular weight asphaltogenic particles having maximum diameters between about 0.5 micron and about 150 microns, said mixing being effected from about 1 second to 24 hours prior to burning.

2. A method of improving the radiation emission of asphaltogenic residual fuel oils during combustion thereof whichcomprises mixing a first residual fuel oil having a precipitation index greater than about 25 with a second residual fuel oil, the fuel oils each comprising a residual oil and a cutter stock having a solvency index of 35-95, the combined distillate cutter stocks present in the mixed oils having a solvency index numerically less than the precipitation index of any residual oil component present therein, said fuel oils being mixed in proportions between about l:4 to about 4:1 on a volume basis, said proportions being suflicient to precipitate between about l% and about 10% by weight of the total fuel components as high molecular weight asphaltogenic particles having maximum diameters between about 0.5 micron and about 150 microns, said mixing being effected from about 1 second to 24 hours prior to burning.

3. A method of improving the radiation emission of asphaltogenic residual fuel oils during combustion thereof which comprises mixing 25-75% by volume of a first residual fuel oil having a precipitation index of about 45-75 with 75-25% by volume of a second residual fuel oil, both of said-fuel pils comprising 50-75 %by weight of distillate cutter stock having;suivafieyfidfarss 95, the solvency index of the combined cutter stocks being numerically less than the precipitation index of said first residual fuel oil, whereby between about 1% and about 10% by weight of the total fuel components precipitate as high molecular weight asphaltogenic particles having maximum diameters between about 0.5 micron and about 150 microns, said mixing being efiected from about 1 second to 24 hours prior to burning.

4. A method of improving the radiation emission of 12 asphaltogenic residual fuels which comprises mixing 25- parts by volume of a first residual fuel oil containing an uncracked residual oil possessing a precipitation index of about 30-40, said residual oil being diluted with a distillate cutter stock having a solvency index greater than the precipitation index of the residual oil, with 75-25 parts by volume of a second residual fuel oil containing a cracked residual oil possessing a precipitation index of about 45-80, said residual oil being diluted with a distillate cutter stock having a solvency index numerically greater than the precipitation index of the cracked residual oil, each of the cutter stocks having a solvency index of 35-95, the two fuel oils being mixed in proportionssuch that the solvency index of the combined cutter stocks is numerically less than the precipitation index of the cracked residual oil, whereby between about 1% and about 10% by weight of the total fuel components precipitate as high molecular tween about 0.5 micron and about microns, said mixing being effected from about 1 second to 24 hours prior to burning.

5. A method of improving the radiation emission of to about 4:1, said proportions being at least sufiicient to produce a mixture of cutter stocks having a solvency index at least about one 'unit less than the precipitation index of any of the residual oil components present, whereby between about 1% and about 10% by weight of the total fuel components precipitate as high molecular asphaltogenic particles, said mixing being effected from 5 seconds to 24 hours prior to burning, whereby 'partic1es"ha'ving maximum'diameters between'about 0.5

micron and about 150 microns are formed.

References Cited in the file of this patent UNITED STATES PATENTS 2,246,760 Ryan et a1. June 24, 1941 2,663,675 Ewell Dec. 22, 1953 2,687,991 Miller Aug. 31, 1954 2,755,229 Beuther et al. July 17, 1956 weight' asphaltogenic particles having maximum diameters be-' substantially free of precipitated l 

1. A METHOD OF IMPROVING THE RADIATION EMISSION OF ASPHALTOGENIC RESIDUAL FUEL OILS DURING COMBUSTION THEREOF WHICH COMPRISES MIXING TWO RESIDUAL FUEL OILS, EACH FUEL OIL COMPRISING A RESIDUAL OIL AND A DISTILLATE CUTTER STOCK HAVING A SOLVENCY INDEX OF 35-95, AT LEAST ONE OF THE RESIDUAL OILS HAVING A PRECIPITATION INDEX GREATER THAN THE SOLVENCY INDEX OF THE COMBINED CUTTER STOCKS SAID FUEL OILS BEING MIXED IN PROPORTIONS BETWEEN ABOUT 1:4 TO ABOUT 4:1 ON A VOLUME BASIS, SAID PROPORTIONS BEING SUFFICIENT TO PRECIPITATE BETWEEN ABOUT 1% AND ABOUT 10% BY WEIGHT OF THE TOTAL FUEL COMPONENTS AS HIGH MOLECULAR WEIGHT ASPHALTOGENIC PARTICLES HAVING MAXIMUM DIAMETERS BETWEEN ABOUT 0.5 MICRON AND ABOUT 150 MICRONS, SAID MIXING BEING EFFECTED FROM ABOUT 1 SECOND TO 24 HOURS PRIOR TO BURNING. 